Exam 2- Gastrointestinal System Flashcards
how does the carnivore digestive tract compare to the herbivore digestive tract?
carnivore: short and simple with expandable stomach
herbivore: fermentation chamber for microbes to digest plants
where does secretion primarily take place in the gastrointestinal system?
stomach and small intestine
where does absorption take place in the gastrointestinal system?
small intestine and some in the large intestine
what is the function of the gastrointestinal tract?
digestion: degrade macromolecules into monomers to be absorbed
synthesize back into macromolecules to be used as energy source
what are the parts of mechanical processing in digestion?
chewing
alternating contraction/relaxation of stomach and small intestine
what is secreted in the secretion step of digestion?
enzyme-containing digestive juices and mucus
what happens during enzymatic breakdown during digestion?
polymers are broken down into monomers by hydrolysis, catalyzed by enzymes
what are the four main processes of digestion?
mechanical processing
secretion
enzymatic breakdown
absorption
what are the four layers of the intestinal wall?
mucosa
submucosa
muscularis
serosa
what cells line the intestinal lumen?
single layer of columnar epithelial
what are the goals of regulation of gastrointestinal function?
completely absorb ingested organic nutrients
restore homeostasis via negative feedback mechanisms
what innervates the gastrointestinal tract?
autonomic nervous system
what do neurons of the intrinsic nervous system synapse with?
each other
smooth muscle and glandular cells
sympathetic and parasympathetic nervous system
what are the two nerves of the parasympathetic system?
vagus nerve (upper GI)
pelvic nerve (lower GI)
what receptors are part of short reflex arcs?
mechanoreceptors (stretch/volume)
chemoreceptors (composition)
are most effector arms of short reflex arcs excitatory/stimulatory or inhibitory?
excitatory/stimulatory (use acetylcholine)
where do sensory (afferent) arms in long reflex arcs orginate?
usually in the gastrointestinal tract
also sensations associated with food
what mediates the effect of long reflex arcs?
enteric motor nerve fibers
sympathetic efferent fibers (reduce blood supply)
do most neurons in the enteric nervous system secrete one or more than one chemical?
more than one
what does acetylcholine cause?
contraction smooth muscle in wall
relaxation sphincters
increased salivary, gastric, and pancreatic secretions
what does norepinephrine cause?
relaxation smooth muscle in wall
contraction sphincters
increased salivary secretion
what does vasoactive intestinal peptide (VIP) cause?
relaxation smooth muscle
increased intestinal and pancreatic secretions
what does nitric oxide (NO) cause?
relaxation smooth muscle
what does gastrin-releasing peptide (GRP), or bombesin, cause?
increased gastric secretion
what are the regulatory substances that can act on target cells in the gastrointestinal tract?
hormones
paracrines
neurocrines
what are the three phases of the regulation of digestive processes?
cephalic phase
gastric phase
intestinal phase
what controls appetite?
hypothalamus
what lines the oral cavity?
stratified squamous epithelium, keratinized in some places
what are the functions of chewing?
mix food with saliva
reduce particle size
mix carbohydrates with salivary amylase
what are the three large paired salivary glands and what does each produce?
parotid- serous
mandibular- serous and mucus
sublingual- serous and mucus
what is saliva composed of?
98% water
ions and organic compounds
what cells in the salivary gland modify the initial saliva?
ductal cells
what do acinar cells do?
form an isotonic plasma-like solution (first step saliva formation)
what do ductal cells do to the saliva?
absorb Na+ and Cl-
secrete K+ and HCO3-
saliva becomes hypotonic (in animals that are not ruminants)
what does saliva do especially for ruminants?
provides urea for protein synthesis
important in pH regulation as well with bicarbonate
under what type of control is salivary secretion?
neural control only
what does sympathetic stimulation cause in salivary glands?
low volume, highly viscous saliva
what type of stimulation dominates during meals?
parasympathetic stimulation
what stimulates the swallowing reflex?
pressure against the pharynx
what are the three phases of swallowing?
oral
pharyngeal
esophageal
what does the primary peristaltic wave do?
moves food down the esophagus
what mediates the secondary peristaltic wave?
local reflexes of the enteric nervous system
what does pepsinogen need to be converted to its active form, pepsin?
HCl and pepsin (can actually go back and make more of itself)
what are the four chambers of the ruminant stomach?
rumen
reticulum
omasum
abomasum
which chamber of the rumen forestomach is analogous to the “true stomach” of a monogastric?
abomasum
when do the reticulorumen and omasum become useful?
when grass consumption begins
what lines the wall of the forestomachs?
stratified squamous epithelium (keratinized)
which chamber of the forestomach is well developed at birth?
abomasum
what is eructation?
belching
what is the purpose of rumen contractions?
mix reticulorumen contents before move to omasum- primary contractions
enable regurgitation as part rumination process- rumination contractions
Enable eructation to remove fermentation gases
what is the first part of the rumen contraction?
first and second reticulum contractions
on second: brief opening reticulo-omasal sphincter so small volume processed content can move into omasum
what initiates eructation?
secondary mixing contraction in rumen contraction
reflexes involved in rumination are initiated by _____________________________ stimulating sensory nerve endings in the digestive tract
course feed fibers
what factors influence rumen contractility?
hypocalcemia
reflex control of reticulorumen contractions: short and long
sensory receptors (mechanoreceptors/stretch and chemoreceptors)
reflex decrease in motility (dissension abomasum, external factors, fever)
what nerves relax the reticulo-omasal sphincter? what do they release?
parasympathetic efferent nerves release vasoactive intestinal peptide (VIP)
what is fermentation?
microbial degradation in the absence of oxygen
what do facultative microbes do?
use up what little oxygen is in the rumen
what are most of the microbes in the rumen?
obligatory anaerobes
what are the three types of primary rumen bacteria?
amylotic: starch and soluble carbohydrates, tolerate acidic conditions
cellulotic: degrade carbohydrates part of plant cell walls, linked by beta-glycosidic bonds
proteolytic
what do secondary rumen bacteria do?
break down products produced by primary bacteria
what are fungi important for in the rumen?
digestion plant fibers, hyphae help to break apart lignin
are protozoa obligate anaerobes or facultative anaerobes?
obligate anaerobes
is there a tunica submucosa in the rumen?
no official one because no muscularis mucosae
is there a muscularis mucosae in the rumen?
no
what chamber of the forestomach has a honeycomb appearance?
reticulum
what makes up the interconnecting folds in the reticulum and what does it produce?
reticular crests create reticular cells
where is there lamina muscularis mucosae in the reticulum?
tips of primary crests
in the omasum, what are the numerous interdigitating folds called?
laminae
how many layers of muscle do the omasal laminae have?
three
Two outer layers extension of muscularis muscosae
inner layer extension of muscularis externa
what cell types can be found in the abomasal glands?
parietal and chief cells
what is in the C1 and C2 parts of the camelid forestomach?
mix of glandular (mucous glands)and nonglandular areas (cornfield stratified squamous epithelium)
what is the distal 1/3 of C3 of the camelid forestomach similar to?
ruminant abomasum- glandular stomach
what does the proventriculus of the avian system do?
glandular stomach: produces HCl and pepsinogen
what cells produce HCl and pepsinogen in the proventriculus?
oxynticopeptic cells
what does the mucosal surface of the ventriculus (gizzard) have?
cuticle of koilin
what two plexuses make up the GI tract intrinsic nervous system?
submucosal and myenteric
what cells make up the lamina epithelialis in the esophagus?
stratified squamous epithelium
what is the lamina propria of the esophagus?
dense connective tissue, abundant elastic fibers
some lymphoid tissue, small vessels and nerves
is the lamina muscularis mucosae always present?
Not always
what does the tunica submucosa of the esophagus contain?
looser connective tissue
large arteries, veins, lymphatics, nerve trunks
mucous or seromucous glands
what lines the gastric cardia?
gastric pits and gastric glands
flat surface converted by surface mucous cells
what cells line gastric pits?
mucous neck cells
where are fundic glands present?
fundus and body of monogastric stomach
where are stem cells in the glandular stomach of monogastrics?
isthmus
what do parietal cells produce?
HCl
what do chief cells produce?
pepsinogen and other enzymes
what is the stratum compactum?
outer dense sheet of collagen fibers in the subglandular layer of carnivores in the stomach
what cell types are in intestinal crypts?
enterocytes
goblet cells
paneth cells
enteroendocrine cells
stem cells
what do enteroendocrine cells do?
secrete more than 20 peptide hormones
true/false: paneth cells are part of innate immunity
true
are there villi in the cecum and colon?
no
what increases surface area in the small intestine?
microvilli and crypts
what percentage of energy in ruminant diets do carbohydrates make up?
85%
in ruminants, what is the preferred pathway for propionate production?
microbes convert pyruvate to propionate directly, not through lactate
at what stage is methane produced in ruminants?
glycolysis: regeneration of NAD+ produces methane as a byproduct (glucose to pyruvate)
how are the total amount and relative proportions of volatile fatty acids affected by feed composition in ruminants (high fiber versus high starch diet)?
high fiber results in lower overall volatile fatty acids, and in each category
high starch increases the amounts of each (butyrate, propionate, and acreage), but propionate especially due to its production with lactate
how are proteins dealt with in ruminants?
extracellularly broken down by microbes into small peptides, small peptides transported into microbes then broken down into amino acids and volatile fatty acids
microbes to small intestine where protein digested and absorbed
can ruminants get sufficient nitrogen from their diet?
no- must supplement to non-protein nitrogen
what happens to non-protein nitrogen, such as urea, in ruminants?
converted to NH4+, to amino acids and proteins (microorganisms do)
urea: paired with fermentable carbohydrates as energy source (also in salivary secretions and blood)
what are the sources of amino acids absorbed in the small intestine of ruminants?
feed proteins not digested by microbes
microbial proteins synthesized in rumen
what do ruminants do with volatile fatty acids in the forestomachs?
almost entirely reabsorbed as important energy source
what is the mechanism for absorption of volatile fatty acids in the forestomachs?
passive cotransport VFA anions for bicarbonate ions: granulosa layer epithelium
passive transport undissociated VFA through keratinized epithelium
what leads to ketosis?
stressful conditions where energy demand > energy supply
nonesterified fatty acids mobilized from adipose tissue, ketone bodies overwhelm metabolic pathway and accumulate
in a healthy ruminant, what happens to ketones after they are absorbed from the forestomach?
energy source rumen epithelial cells
also to cardiac and skeletal muscle
the hepatic acinus is the _______________________________
functional unit of the liver
what do satellite cells (“perisinusoidal cells”, pericytes) do?
storage vitamin A
liver damage activates to produce extracellular matrix
why are bile salts needed?
emulsify lipids because would be insoluble, so would products of lipid digestion
what do bile salts do?
emulsify lipids then solubility the products of lipid digestion into packets called micelles
what are bile salts?
bile acids conjugated to glycine or taurine
what makes the constituents of bile?
hepatocytes
what stimulates the gall bladder to contract and the sphincter of Oddi to relax so that bile is released into the lumen of the duodenum?
presence of fats in small intestine leads to cholecystokinin release
true/false: biles salts stay in the small intestine throughout its length, then are reabsorbed into the portal vein and extracted by hepatocytes and are reused
true
true/false: bile salts are passively reabsorbed in the ileum
false: sodium-dependent secondary active transport
how is the passive reabsorption of bile acids reduced in the small intestine?
conjugation into bile salts
what two primary bile acids are conjugated by hepatocytes from cholesterol?
cholic acid
chenodeoxycholic acid
how are the bile acids made more water soluble?
conjugated into bile salts
what do intestinal bacteria do to the primary bile acids?
modify to make secondary bile acids:
deoxycholic acid
lithocholic acid
what are the functions of the gall bladder?
store bile
concentrate bile
eject bile
how does the gall bladder concentrate bile?
epithelial cells absorb water and ions
what species have continuous or almost continuous bile flowing into the small intestine and therefore do not need a bile-concentrating mechanism?
horses and rats continuous
ruminants- gallbladder has short retention time
what happens to erythrocytes as they age?
get beat up and become less flexible
what do macrophages do to old erythrocytes?
phagocytose them
degrade hemoglobin
converts heme to bilirubin
what happens to bilirubin?
extracted by liver from blood, secreted into bile
in small intestine: bilirubin to urobilingoen
urobilinogen into urine
what proteins does the liver synthesize?
glutathione
albumin
clotting factors
C-reactive protein
carrier proteins
hormones and prohormones
apolipoproteins
what are the metabolic functions of the liver?
carbohydrate metabolism
protein metabolism
lipid metabolism
what are the phases in the liver modifying endogenous and exogenous toxins?
phase I: conversion reaction with enzymes in hepatocytes endoplasmic reticulum (cytochrome P450 enzyme)
phase II: conjugation of substances to facilitate excretion
what is First Pass Metabolism?
orally administered drugs are metabolized by liver before entering general circulation
what do Kupffer cells do in innate immunity?
phagocytose large particles (microbes, cancer cells, cell fragments, damaged erythrocytes)
what do endothelial cells do in innate immunity?
receptor-mediated endocytosis (macromolecules from extracellular matrix, immune complexes)
what does phagocytosis lead to?
production cytokines and acute phase proteins (role in immune cell recruitment and activation)
the liver is the only visceral organ with the capacity for _________________________
compensatory hyperplasia
what is the mechanism of liver regeneration?
activation numerous gene pathways in healthy hepatocytes
production cytokines and growth factors
hepatocyte proliferation
what are the four types of contractions in the large instestine?
segmentation
peristalsis
antiperistalsis
mass movements
what almost functions like the sphincter between the stomach and small intestine in horses?
the pelvic flexure
how does water get absorbed in the intestine?
follows transport solutes
mucosa freely permeable to water
what are the cells that line the intestines and do fluid and water transport?
enterocytes
what does free iron bind to in the intestines?
ferritin (intracellular storage form)
how is iron transported across the basolateral membrane?
ferroportin
is iron ingested as part of a heme molecule more bioavailable or less than iron ingested as non-heme iron?
more, due to factors that interfere with absorption in non-heme iron
how does vitamin C increase the absorption of iron?
reduces it from Fe3+ to Fe2+
via what routes it calcium absorbed?
paracellular and transcellular
how is calcium transported via the transcellular route in the intestines?
Ca-ATPase pump and Ca/Na exchanger
in the jejunum, is sodium moved passively or actively?
active transport mechanisms
what is the net movement of NaCl in the ileum?
net absorption of NaCl
what promotes Na+ absorption in the large intestine?
aldosterone
in what species is absorption of water and salt in the large intestine extra important?
hindgut fermenters
on what ion is water and solute secretion in the intestine dependent on?
chloride
what are the types of diarrhea?
decreased surface area for absorption
osmotic
secretory
how does diarrhea affect the electrolytes in the body?
by increasing flow through the intestine
hypokalemia
metabolic acidosis
how is digestion carried out in the large intestine?
microbial enzymes, not secreted enzymes
what do glands produce in the large intestine?
bicarbonate and mucin
do enterocytes (large intestine) have microvilli?
no
what does fermentation of carbohydrates produce (in large intestine)?
volatile fatty acids
what does the large intestine do with volatile fatty acids?
absorbs them and uses as energy source (including for epithelial cells)
do hindgut fermenters digest microbes as a source of protein?
no
what is coprophagy?
rabbits and rats eat fecal clumps
allows digestion components of microorganisms
why do ruminants obtain more energy per a given amount of cellulose than horses?
long retention time of feed particles in forestomachs
fermentation chamber before small intestine leads to more complete absorption of volatile fatty acids
ability to digest microbial proteins
what regulates the contractions of the large intestine and emptying of the rectum?
interstitial cells of cajal
is the autonomic influence on the interstitial cells of cajal stronger or weaker than the autonomic influence in the stomach and small intestine?
stronger
what does the secretion from the exocrine pancreas comprise of?
bicarbonate and enzymes
how much of the pancreatic mass does the exocrine pancreas make up?
90-98%
what is the function of the bicarbonate secreted from the exocrine pancreas?
neutralizes H+ delivered to duodenum by stomach
what is the function of the enzymes secreted by the exocrine pancreas?
digest carbohydrates, proteins, and lipids
are enzymes and aqueous components secreted separately or together from the exocrine pancreas?
separately
what cells secrete enzymes from the exocrine pancreas?
acinar cells
what cells secrete aqueous components from the exocrine pancreas?
centroacinar and ductal cells
________________ enzymes are released as inactive proenzymes
proteolytic
pancreatic gland cells also produce ________________________ as a safeguard against digesting themselves
trypsin inhibitor
what are the ions in the aqueous solution secreted by the exocrine pancreas?
Na+
K+
Cl-
HCO3-
what ions in exocrine pancreatic aqueous solution are influenced by flow rate and which ones are not?
HCO3- and Cl- influenced by flow rate
Na+ and K+ do not change
what are the two major functions of pancreatic juice?
prevents injury to duodenal mucosa and provides optimal pH for pancreatic enzymes with high pH
enzymes degrade digestible molecules
what stimulates release of cholecystokinin from the I cells of the duodenal epithelium?
nutrients in the lumen of the small intestine
acinar cells have receptors for ____ and ____
cholecystokinin
acetylcholine
ductal cells have receptors for ____, ____, and ____
cholecystokinin
acetylcholine
secretin
what is the major stimulant of bicarbonate-rich secretion?
release of secretin by S cells of duodenal epithelium
stimulated by acid contents
cholecystokinin is released in response to ________________________________
degradation products of fat and protein in small intestine
what is a “Glisson’s capsule?”
hepatic capsule
underlying connective tissue layer containing small blood vessels, nerves, and lymphatics
what are portal triads?
small areas of dense irregular connective tissue that contains branches of the hepatic artery and portal vein, bile ducts, and lymph channels
what connective tissue is found throughout most of the liver?
reticular connective tissue
what percentage of cells in the liver are hepatocytes?
80%
are hepatocytes able to by polyploidy?
yes, frequently are
what surfaces of hepatocytes have microvilli?
apical surfaces, facing perisinusoidal space
can hepatocytes store lipid droplets?
yes
what is plentiful in hepatocytes?
both rough and smooth endoplasmic reticulum
golgi membranes, especially near bile canaliculi
what is the dual blood supply to the liver?
portal vein: nutrient and hormone rich, oxygen poor
hepatic artery: highly oxygenated
where does the arterial and venous blood mix in the liver?
sinusoids
how does blood leave the liver?
collected by central vein out of sinusoids
sublobar veins
hepatic vein
what lines the bile ducts in the liver?
simple cuboidal epithelium
what lines sinusoids?
discontinuous and fenestrated endothelium
what are the three zones of hepatic parenchyma?
periportal zone: closest to portal triads (1)
centrilobular zone: closest to central vein (2)
midzonal area: between (3)
what are periportal zone hepatocytes specialized for?
oxidative liver functions
what is the space of disse?
between hepatocytes and sinusoid
what cells are in the space of disse?
stellate cells (Ito cells)
what do stellate cells (Ito cells) do?
produce extracellular matrix components of space of disse
secrete cytokines
vitamin A storage and storage of other lipid-soluble vitamins
what are Kupffer cells?
resident liver macrophages in sinusoids
phagocytosis
what are bile canaliculi?
minute spaces between apposed hepatocytes formed by tight junctions
true/false: the direction of bile flow is the same direction as blood flow
false: opposite directions
bile ductules are lined by low, simple cuboidal epithelium (______________)
cholangiocytes
does the gall bladder have a muscularis mucosae and submucosa?
no
how can the small intestine and gall bladder be distinguished?
small intestine has crypts, gall bladder does not
why is intrinsic factor an essential component of gastric secretion?
required for absorption of vitamin B12
what do parietal cells secrete?
HCl and intrinsic factor
what cells secrete pepsinogen?
chief cells
what cells secrete pepsin?
none- pepsinogen is secreted then activated
where do stimulatory and inhibitory mechanisms for gastric contractions originate?
stimulatory: stomach
inhibitory: duodenum
what are the two types of small intestinal contractions?
mixing (segmental contractions)
propulsion of contents (peristalsis)
what reflexes play the primary role in small intestine motility (parasympathetic, hormonal, local reflexes)?
local reflexes
some parasympathetic
expansion of small intestine stimulates release of ____________ from ECL cells of small intestinal mucosal epithelium
serotonin
what does parasympathetic activity via the vagus nerve lead to in the small intestine?
increased contractile strength
are mixing contractions or peristaltic contractions predominating when digestive processes are occurring in carnivores and omnivores?
mixing contractions predominate
what increases surface area in the small intestine?
microvilli
folds
villi
how are things absorbed in the small intestine?
transcellular (primary by far)
paracellular
what are the two phases of carbohydrate breakdown into monomers in the small intestine?
luminal phase (starch and glycogen into poly- and disaccharides by amylase) (ruminants very little amylase in pancreatic secretions)
membranous phase (simple into monosaccharides)
how are glucose and galactose absorbed?
sodium-dependent co-transport, secondary active
how is fructose absorbed?
facilitated diffusion
in what forms can nutrients from proteins be absorbed?
amino acids
dipeptides
tripeptides
where are proteins digested?
stomach and small intestine
how are protein products absorbed in the small intestine?
coupled to sodium or hydrogen ions
the presence of fat in the duodenum causes release of ______________, which leads to slowing gastric emptying to allow time for fat digestion
cholecystokinin
bile salts ______________ the fat into droplets, as the ____________ step of lipid degradation
emulsify
first
true/false: lipids are released at the apical membrane from the bile salts and diffuse down their concentration gradient
true
what is the sequence of cells for saliva formation?
acinar cells form initial
ductal cells modify
myoepithelial contract to eject
are ductal cells in saliva formation water permeable?
no
rate of saliva production being low leads to ____________ osmolarity than blood
lower
what is the afferent arm for the swallowing reflex?
vagus and glossopharyngeal nerves
what are the receptors and nerves involved in the swallowing reflex?
sensory receptors wall of pharynx
afferent arm- vagus and glossopharyngeal nerves
integration in medullary swallowing center
efferent arm- motor nerves to striated muscles in upper esophagus and pharynx
the hard and soft palate’s dorsal surface has ______________________________ cells
pseudostratified ciliated columnar
what produces dentine?
odontoblasts
what are the tubular spaces in dentine called?
dentinal tubules
__________________ is the layer between the periodontal ligament and the dentin
cementum
chloride channels open in response to binding of various hormones and neurotransmitters on the basolateral membrane: ____________________
acetylcholine and vasoactive intestinal peptide
how can kupffer cells activate stellate cells?
secrete cytokines
are islets of Langerhans exocrine or endocrine in the pancreas?
endocrine
what are the five neurotransmitters of the GI tract?
acetylcholine
nitric oxide
GRP
norepinephrine
vasoactive intestinal peptide
what are the hormonal regulators of the GI tract?
gastrin
secretin
cholecystokinin
gastrointestinal peptide
somatostatin (paracrine)
histamine (paracrine)
